Terminal, base station, transmission method, and reception method

ABSTRACT

A reception processor receives the cell detection reference signals, each of the cell detection reference signals being transmitted from corresponding one of a plurality of cells. An RRM report generator generates measurement information indicating a measurement result of reception quality measured using the cell detection reference signal. A transmission processor transmits the measurement information. The cell detection reference signals are mapped to any one of a plurality of candidate resources, which is a part of a plurality of resources set for other reference signals in a subframe to which the cell detection reference signals are mapped.

BACKGROUND Technical Field

The present disclosure relates to a terminal, a base station, atransmission method, and a reception method.

Description of the Related Art

In an LTE-Advanced technique, which is further enhanced from a 3rdGeneration Partnership Project Radio Access Network Long Term Evolution(3GPP-LTE; hereinafter, referred to as LTE), accommodating increasedtraffics as described below is considered. That is to say, in an areacovered by macro cells that are base stations with high transmissionpowers (referred to as eNBs), small cells that are base stations withlow transmission powers (referred to as low power nodes (LPN) in somecases) are arranged in high density.

For operating the high-density arrangement of small cells, control ofthe on state and the off state of the small cells is considered in orderto suppress interference caused by the small cells and to reduce thepower consumed by the small cells. When the small cells are in the offstate, the small cells are in a “halt state” in which data is notallocated to a terminal (user equipment (UE)).

However, when transmission of all signals from a small cell is stopped,the terminal cannot detect the small cell any more. To prevent this,causing the small cell to transmit a cell detection reference signal(referred to as discovery signal in some cases) is considered so thatthe terminal can detect a small cell in the off state. The small celltransmits the cell detection reference signal to the terminal to cause anetwork to report a measurement result in the terminal. With this, abase station can appropriately set a cell connection of the terminaltaking into account propagation path conditions between the terminal andthe small cells or traffic conditions of each small cell.

The cell detection reference signal is a signal for performing celldetection in the terminal, time frequency synchronization, andmeasurements for radio resource management (RRM) of same frequencies anddifferent frequencies when the small cell is in the off state. Tosuppress interference with the terminal and the power consumed by thesmall cell, the cell detection reference signal is desired to betransmitted from the small cell with long transmission intervals.Furthermore, for the measurements for RRM to be performed in theterminal, causing the transmission interval of the cell detectionreference signal to be notified in advance from the network isconsidered.

The small cell in the off state transmits only the cell detectionreference signal and does not transmit any other signals. Therefore, anexisting terminal (legacy UE supporting the standard specification forRel. 11 or before, for example) cannot use the cell detection referencesignal for the measurements for RRM. By contrast, a new terminal (UEsupporting the standard specification for Rel. 12, for example) respondsto the measurements for RRM using the cell detection reference signalfor the purpose of enhancement of small cells, and thus can observe thecell detection reference signal. Furthermore, the small cell in the onstate transmits the cell detection reference signal together withsynchronization signals (primary synchronization signal (PSS)/secondarysynchronization signal (SSS)) or cell specific reference signal (CRS).With this, the existing terminal and the new terminal both can observe asignal.

Furthermore, as a configuration of the cell detection reference signal,changing the cycle, the band (that is, time and frequency resources),and the like of a signal already present in an LTE-Advanced system foruse is considered. As a candidate signal used as a cell detectionreference signal, a positioning reference signal (PRS), a channel stateinformation-reference signal (CSI-RS), a reduced PSS/SSS+CRS, and thelike are cited (see 3GPP TSG RAN WG1 meeting, R1-133457, NTT DOCOMO,“Small Cell Discovery for Efficient Small Cell On/Off Operation”, August2013, for example).

As an example, a case where the CSI-RS is applied for the cell detectionreference signal will be herein described.

The CSI-RS is a signal introduced for the purpose described below. Aterminal uses the CSI-RS to observe channel information from a basestation to the terminal and generates a feedback signal in accordancewith the observed value to report to the base station. The base stationperforms adaptive modulation, precoding control, or the like based onthe feedback signal. The CSI-RS is defined in a configurationcorresponding to a maximum 8-port transmission antenna of the basestation (see 3GPP TS36.211v11.4.0 (2013-09), “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical channels and modulation(Release 11)”, September 2013, for example). More specifically, theCSI-RS is defined in each of configurations for 8 ports, 4 ports, and 2ports in accordance with the number of the transmission antenna ports ofthe base station.

BRIEF SUMMARY

When simply combining existing reference signals such as a CSI-RS as acell detection reference signal, a problem as described below arises.Specifically, in order to improve the detection accuracy of a celldetection reference signal in a terminal, the resource for transmittingthe cell detection reference signal is desirably not used for datatransmission. For this reason, the more the number of small cellsarranged at high density is, the resource usable for data transmissionis decreased in the resource for transmitting the cell detectionreference signal. The frequency use efficiency in a subframe in whichthe cell detection reference signal is arranged thus is lowered. Themore the number of small cells per macro cell is, for example, 20 to 100cells, the more remarkable this problem becomes.

One non-limiting and exemplary embodiment provides a terminal, a basestation, a transmission method, and a reception method that are capableof preventing lowering of the frequency use efficiency in a subframe inwhich the cell detection reference signal is arranged.

In one general aspect, the techniques disclosed here feature a terminalincluding a reception processor, a generator, and a transmissionprocessor. The reception processor receives first reference signals,each of the first reference signals being transmitted from correspondingone of a plurality of cells. Each of the first reference signals is areference signal for cell detection that is mapped to any one of aplurality of candidate resources, which are a part of a plurality ofresources set for second reference signals in a subframe. The generatorgenerates measurement information indicating a measurement result ofreception quality measured using the received first reference signal.The transmission processor transmits the generated measurementinformation.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof

According to the present disclosure, lowering of the frequency useefficiency in a subframe in which the cell detection reference signal isarranged can be prevented.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1A to 1C are diagrams each illustrating a configuration example ofa resource in which a CSI-RS is arranged;

FIG. 2 is a block diagram illustrating a main configuration of a basestation according to a first embodiment of the present disclosure;

FIG. 3 is a block diagram illustrating a main configuration of aterminal according to the first embodiment of the present disclosure;

FIG. 4 is a block diagram illustrating a configuration of the basestation according to the first embodiment of the present disclosure;

FIG. 5 is a block diagram illustrating a configuration of the terminalaccording to the first embodiment of the present disclosure;

FIG. 6 is a diagram illustrating a setting example of a non-transmissionsignal resource;

FIG. 7A is a diagram illustrating a CSI-RS configuration according to asecond embodiment of the present disclosure (in a case of 2 antennaports);

FIG. 7B is a diagram illustrating a CSI-RS configuration according tothe second embodiment of the present disclosure (in a case of 4 antennaports);

FIG. 7C is a diagram illustrating a CSI-RS configuration according tothe second embodiment of the present disclosure (in a case of 8 antennaports); and

FIG. 8 is a diagram illustrating an example of a system configurationaccording to a third embodiment of the present disclosure.

DETAILED DESCRIPTION Underlying Knowledge Forming Basis of the PresentDisclosure

FIGS. 1A to 1C are diagrams each illustrating a configuration example ofa resource in which a CSI-RS is arranged in a subframe. FIG. 1A is aconfiguration example with the number of antenna ports of 8 ports. FIG.1B is a configuration example with the number of antenna ports of 4ports. FIG. 1C is a configuration example with the number of antennaports of 2 ports. In FIGS. 1A to 1C, one subframe is formed by tworesource blocks (RB) with 12 subcarriers bundled together. Furthermore,in FIGS. 1A to 1C, #i (0 to 19) is a CSI-RS configuration numberrepresenting a resource (2 resource element (2RE)) including twoorthogonal frequency division multiplexing (OFDM) symbols continuing ina time domain in each subcarrier. In each resource (2RE), CSI-RSs fortwo ports are code multiplexed.

Each terminal acquires in advance information on the CSI-RS from thebase station through a higher layer. Specific examples of theinformation on the CSI-RS are cited below. A numbers of antenna ports(antennaPortsCount), a CSI-RS configuration number specifying thesubcarrier in the subframe and the position of the OFDM symbol(resourceConfig: #0 to #19 in FIGS. 1A to 1C for example), atransmission subframe including a transmission cycle and an offset(subframeConfig), a power ratio of a reference signal to a data signal(p-C), and the like are cited as the examples.

In FIGS. 1A to 1C, the CSI-RS configuration numbers are assigned in theorder in the time axis (horizontal axis) direction, and in the order inthe frequency axis (vertical axis) direction for the same time axis. Asillustrated in FIGS. 1A to 1C, among the

CSI-RS configurations corresponding to each number of antenna ports, astart position of the resource of each CSI-RS configuration numbers(start position in the order of number assignment) is assigned with thesame number. Furthermore, as illustrated in FIGS. 1A to 1C, a CSI-RSconfiguration in a case where the number of antenna ports is small formsa subset of a CSI-RS configuration in a case where the number of theantenna ports is large.

With this, while using duplicated number assignment in the CSI-RSconfigurations corresponding to each number of antenna ports,specification of the resource for each number of antenna ports can beperformed with minimum required CSI-RS configuration numbers. Forexample, the CSI-RS configuration number #0 for 2 ports illustrated inFIG. 1C can be specified as only resources for 2 ports (2RE) from thestart point, out of the resources (8RE) represented by the CSI-RSconfiguration number #0 for 8 ports illustrated in FIG. 1A.

As described above, to observe channel information between each basestation and the terminal to be subjected to adaptive modulation andprecoding control, a procedure is taken in which the base stationnotifies the terminal of information on the CSI-RS in advance. When theCSI-RS is used as the cell detection reference signal, it is alsopossible that a network formed of a plurality of base stations notifiesthe terminal of predefined information in advance. For example, withinformation such as the above-described CSI-RS configuration number anda transmission subframe notified in advance from the network to theterminal, the terminal side can perform signal measurement for celldetection.

The applicant has found from earnest research based on theabove-described knowledge that a configuration with a cell detectionreference signal arranged in any of candidate resources being a part ofa plurality of resources set for arranging other reference signal (forexample, a CSI-RS) in the subframe in which the cell detection referencesignal is arranged, can prevent lowering of the frequency use efficiencyin the subframe in which the cell detection reference signal isarranged.

Embodiments according to the present disclosure will be described belowin detail with reference to the drawings. It should be noted that thesame components are assigned with the same reference characters and anyrepeated description thereof is omitted.

First Embodiment

In an LTE technique and an LTE-Advanced technique, orthogonal frequencydivision multiple access (OFDMA) is employed as a downlink communicationmethod. As a transmission method of a cell detection reference signal inthe OFDMA, transmitting a signal using a predetermined OFDM symbol and apredetermined subcarrier is considered.

With this, a terminal can grasp a transmission position of the signal aslong as synchronization is secured between the terminal and a cell to bemeasured. This further enables observation of a reception signal powerof the cell detection reference signal (referred to as a referencesignal reception power (RSRP) in some cases) or a reception signalquality (referred to as a reference signal reception quality (RSRQ) insome cases).

On the other hand, securing a predetermined time or more during whichdata transmission and reception are not performed can stop theoperations of a transmitter and a receiver and thereby provide a powersaving effect with the terminal (discontinuous reception (DRX)). Forthis operation, to minimize the interval length in which the terminalneeds to perform a reception operation and secure a predetermined timeor more during which data transmission and reception is not performed, aconfiguration as described below is considered. In a configuration ofthe network, the reference signals for cell detection transmitted by aplurality of cells are concentratedly arranged in a predeterminedsubframe and the terminal can perform DRX in other subframes for alonger period of time. That is to say, more reference signals for celldetection are required to be arranged in a predetermined subframe.

Outline of Communication System

A communication system according to the first embodiment of the presentdisclosure includes a base station 100 and a terminal 200. The basestation 100 is a base station corresponding to an LTE-Advanced systemand the base station 200 is a terminal corresponding to an LTE-Advancedsystem.

FIG. 2 is a main configuration diagram of the base station 100 accordingto the first embodiment of the present disclosure. In the base station100, a setter 101 sets information on a subframe in which the celldetection reference signal is arranged. A transmission processor 104transmits the above-described information. A reception processor 108receives an RRM report (measurement information) indicating ameasurement result of reception quality (RSRP or RSRQ) measured usingthe cell detection reference signal.

FIG. 3 is a main configuration diagram of the terminal 200 according tothe first embodiment of the present disclosure. In the terminal 200, areception processor 203 receives the cell detection reference signal. AnRRM report generator 206 generates the RRM report (measurementinformation) indicating a measurement result of reception quality (RSRPor RSRQ) measured using the cell detection reference signal. Atransmission signal former 208 transmits the RRM report.

The cell detection reference signal is arranged in any of candidateresources being a part of a plurality of resources set for arrangingother reference signal (for example, a CSI-RS) in the subframe in whichthe cell detection reference signal is arranged.

Configuration of Base Station 100

FIG. 4 is a block diagram illustrating a configuration of the basestation 100 according to the first embodiment of the present disclosure.In FIG. 4, the base station 100 includes the setter 101,coders/modulators 102, 103, the transmission processor 104, transmitters105-1, 105-2, antennas 106-1, 106-2, receivers 107-1, 107-2, thereception processor 108, a data receiver 109, and an RRM report receiver110.

The setter 101 generates information on the cell detection referencesignal (cell detection reference signal information) with respect to theterminal 200 to be subjected to the RRM report. The cell detectionreference signal information includes transmission subframe informationincluding a transmission cycle and an offset, for example. That is tosay, the setter 101 sets a subframe in which the cell detectionreference signal is arranged. The setter 101 thus sets a parameterrequired for measuring the reception signal power (RSRP) and thereception signal quality (RSRQ) for each cell, with respect to theterminal 200 to be subjected to the RRM report.

The cell detection reference signal information generated by the setter101 is transmitted, as control information (setting information), to theterminal 200 to be subjected to the RRM report after receivingtransmission processing in the coder/modulator 102, the transmissionprocessor 104, and the transmitter 105. As control information forproviding a notification of the cell detection reference signalinformation, information on radio resource control (RRC signaling) canbe used.

The setter 101 generates assignment control information includingresource block (RB) assignment information and information on amodulation and coding scheme (MCS) with respect to one or more transportblock (TB). The assignment control information includes assignmentcontrol information on upstream resource to which uplink data isassigned (for example, physical uplink shared channel (PUSCH)) andassignment control information on downstream resource to which downlinkdata is assigned (for example, physical downlink shared channel(PDSCH)). The assignment control information is output to thetransmission processor 104 and the reception processor 108, and at thesame time, notified to the terminal 200 from the base station 100through PDCCH.

The coder/modulator 102 codes and modulates information received fromthe setter 101 and outputs a modulation signal thus obtained to thetransmission processor 104.

The coder/modulator 103 codes and modulates a data signal (transmissiondata) being input and outputs a modulation signal thus obtained to thetransmission processor 104.

The transmission processor 104 forms a transmission signal by mappingthe modulation signal received from the coder/modulator 102 and thecoder/modulator 103 to a resource indicated by the assignment controlinformation on downstream resource received from the setter 101. Thetransmission signal including the cell detection reference signalinformation is thus transmitted. At this time, when the transmissionsignal is an OFDM signal, the transmission processor 104 maps themodulation signal to the resource indicated by the assignment controlinformation on downstream resource received from the setter 101,transforms the mapped signal into a time waveform through inverse fastFourier transform (IFFT) processing, and adds a cyclic prefix (CP) tothe converted waveform, whereby the OFDM signal is formed.

The transmitter 105-1 or 105-2 performs transmission radio processing(upconversion, digital/analog (D/A) conversion, and the like) on thetransmission signal received from the transmission processor 104 andtransmits the signal thus obtained through the antenna 106-1 or 106-2.

The receivers 107-1 and 107-2 perform reception radio processing(downconversion, analog/digital (A/D) conversion, and the like) on aradio signal received through the antenna 106-1 or 106-2 and output areception signal thus obtained to the reception processor 108.

With respect to the transmitters, receivers, and antennas provided inplurality, an operation in which the transmitter 105-1, the receiver107-1, and the antenna 106-1 are used for forming a macro cell and thetransmitter 105-2, the receiver 107-2, and the antenna 106-2 are usedfor forming a small cell is possible, for example. Furthermore, thenumber of the transmitters, the receivers, and the antennas is notlimited to two as illustrated in FIG. 4, and may be three or more.

The reception processor 108 specifies a resource to which an upstreamdata signal and ACK/NACK information are mapped based on the resourceassignment control information received from the setter 101 and extractsa signal component mapped to the specified resource from the receptionsignal. The reception processor 108 further extracts the RRM report fromthe reception signal.

At this time, when the reception signal is an OFDM signal, the receptionprocessor 108 transforms the extracted signal component into a timedomain signal by performing inverse discrete Fourier transform (IDFT)processing thereon.

The upstream data signal (reception data) and the ACK/NACK informationthus extracted by the reception processor 108 are output to the datareceiver 109, and the RRM report is output to the RRM report receiver110.

The data receiver 109 decodes the signal received from the receptionprocessor 108. The uplink data and the ACK/NACK information are thusobtained.

The RRM report receiver 110 outputs the signal received from thereception processor 108 to other components (not illustrated). The basestation 100 performs operations such as selection of connection cellsfor the terminal 200 to be subjected to the RRM report based on thereceived RRM report for each cell.

Configuration of Terminal 200

FIG. 5 is a block diagram illustrating a configuration of the terminal200 according to the first embodiment of the present disclosure.

In FIG. 5, the terminal 200 includes an antenna 201, a receiver 202, thereception processor 203, a reference signal generator 204, a data signalgenerator 205, the

RRM report generator 206, a transmission controller 207, thetransmission signal former 208, and a transmitter 209.

The receiver 202 performs reception radio processing (downconversion,analog/digital (A/D) conversion, and the like) on a radio signalreceived through the antenna 201 and outputs a reception signal thusobtained to the reception processor 203.

The reception processor 203 extracts setting information, assignmentcontrol information, and a data signal contained in the receptionsignal. The reception processor 203 outputs the assignment controlinformation to the transmission controller 207 and outputs the settinginformation to the RRM report generator 206. The reception processor 203further performs error detection processing on the extracted data signaland outputs the ACK/NACK information in accordance with a result of theerror detection to the data signal generator 205.

The reception processor 203 further specifies a transmission subframe towhich the cell detection reference signal is transmitted, based on thecell detection reference signal information included in the settinginformation. The reception processor 203 then extracts the celldetection reference signal (for example, a CSI-RS) transmitted from eachcell from the reception signal in the specified transmission subframeand outputs a reception value of the cell detection reference signal tothe RRM report generator 206.

Upon receiving a generation instruction from the transmission controller207, the reference signal generator 204 generates a reference signal andoutputs the generated reference signal to the transmission signal former208.

The data signal generator 205, using the ACK/NACK information and thetransmission data serving as inputs, codes and modulates the ACK/NACKinformation and the transmission data based on MCS information receivedfrom the transmission controller 207 to generate a data signal. Itshould be noted that when the reception signal is an OFDM signal, thedata signal generator 205 also performs CP removal processing and FFTprocessing.

The RRM report generator 206 generates an RRM report using the celldetection reference signal (reception value) received from the receptionprocessor 203. Specifically, the RRM report generator 206 uses the celldetection reference signal to measure the reception signal power (RSRP)or the reception signal quality (RSRQ) and generates the RRM report(measurement information) indicating a measurement result. The RRMreport generator 206 outputs the generated RRM report to thetransmission signal former 208.

The transmission controller 207 specifies a “data mapping resource” towhich a data signal is mapped based on the assignment controlinformation received from the reception processor 203 and outputsinformation on the data mapping resource (hereinafter, referred to as“data mapping resource information” in some cases) to the transmissionsignal former 208, and at the same time, outputs MCS informationincluded in the assignment control information to the data signalgenerator 205.

The transmission signal former 208 maps the reference signal receivedfrom the reference signal generator 204 to a mapping resource for areference signal. The transmission signal former 208 further maps thedata signal received from the data signal generator 205 to the datamapping resource indicated by the data mapping resource information. Thetransmission signal former 208 further maps the RRM report received fromthe RRM report generator 206 to a mapping resource for the RRM report. Atransmission signal is thus formed. With this, a transmission signalincluding the RRM report is transmitted. It should be noted that whenthe transmission signal is an OFDM signal, the transmission signalformer 208 performs discrete Fourier transform (DFT) on the data signalbefore mapping the data signal to the data mapping resource.Furthermore, a CP is added to the transmission signal thus formed.

The transmitter 209 performs transmission radio processing(upconversion, digital/analog (D/A) conversion, and the like) on thetransmission signal formed in the transmission signal former 208 beforetransmitting the transmission signal through the antenna 201.

Operation of Base Station 100 and Terminal 200

Operations performed by the base station 100 and the terminal 200 havingthe above-described configurations will be described below.

In the description below, unless otherwise specified, the cell detectionreference signal is to be transmitted over the entire system band in thetransmission subframe of the cell detection reference signal.

Furthermore, in the description below, as an example of a resource forarranging the cell detection reference signal, a case where a part ofresources set for arranging CSI-RSs is used will be described.

In the base station 100, the setter 101 generates transmission subframeinformation indicating the subframe for transmitting the cell detectionreference signal to the terminal 200 to be subjected to the setting. Thetransmission subframe information includes parameters corresponding tothe transmission cycle and the offset, for example.

The transmission subframe information is notified from the base station100 to the terminal 200 in advance and thereby shared between the basestation 100 and the terminal 200.

The base station 100 thus notifies the terminal 200 of the informationon the cell detection reference signal, and thereby causes the terminal200 to implement the RRM report using the cell detection referencesignal.

For example, the base station 100 practices a rule as described belowwith respect to the terminal 200, and thereby is able to obtain the RRMreport from the terminal 200. For example, a rule is set up to stipulatethat, at a time point in which an event occurs that has beenpredetermined with respect to a measurement result of the receptionsignal power (RSRP) or the reception signal quality (RSRQ) when the celldetection reference signal is received, the RRM report is fed back.Alternatively, a rule is set up to stipulate that measurement resultsfor all cells exceeding predetermined reception signal power orreception signal quality are to be reported. Examples of thepredetermined event will be cited below. One example is a case where ameasurement result of the reception signal power or the reception signalquality when the cell detection reference signal is received from acertain cell exceeds a predetermined threshold. Another example is acase where a measurement result of the reception signal power or thereception signal quality when the cell detection reference signal isreceived from a certain cell is within a predetermined level differencecompared with the reception signal power or the reception signal qualityof a cell to which the terminal 200 belongs. Still another example is acase where a measurement result of the reception signal power or thereception signal quality when the cell detection reference signal isreceived from a certain cell exceeds a predetermined level differencecompared with the reception signal power or the reception signal qualityof a cell to which the terminal 200 belongs.

Out of a plurality of resources set for the CSI-RS (see FIGS. 1A to 1C,for example), the base station 100 and the terminal 200 use only a partof the resources that has been predetermined as the resource for thecell detection reference signal. That is to say, the cell detectionreference signal transmitted from each cell is arranged in any of aplurality of resources (candidate resources) being a part of a pluralityof resources set for arranging the CSI-RS.

For example, as the resources set for the CSI-RS, there are 40 resourcesin total that are composed by multiplication of two types of spreadcodes ({+1, +1}, {+1, −1}) for multiplexing two ports with each of theresources represented by the CSI RS configuration numbers and other 20resources usable for 2-port CSI-RSs represented by the CSI-RSconfiguration numbers (#0 to #19 illustrated in FIG. 1C).

The base station 100 and the terminal 200 limit the resource for celldetection reference signal (candidate resource) to a part of these 40resources. For example, the base station 100 and the terminal 200 limitthe candidate resource to 10 resources with smaller CSI-RS configurationnumbers (#0 to #9) out of the 20 resources represented by 20 CSI-RSconfiguration numbers. In this case, the base station 100 and theterminal 200 use only 20 resources in total, out of the 40 resources,including the limited 10 resources (represented by CSI-RSs #0 to #9) andthe resources formed by combination with two types of spread codes, asthe candidate resources for the cell detection reference signal.

The base station 100 and the terminal 200 further specifies a resourcein which the cell detection reference signal transmitted from each cellis arranged based on the cell identification number (Cell ID) of eachcell, out of the part of the resources (20 resources in the exampleabove). For example, the resource for the cell detection referencesignal for each cell is specified as a resource corresponding to a value(V_(shift)) (V_(shift)=0 to 19) obtained by using the cellidentification number (Cell ID) to set mod(Cell ID, 20).

At this time, in an LTE technique, Cell ID is to be an optional valuefrom 0 to 503. Furthermore, in the example above, it is assumed thatV_(shift)=0 to 9 is respectively associated with the combination of eachof the CSI-RS configuration numbers #0 to #9 and the spread code {+1,+1}, and V_(shift)=10 to 19 is respectively associated with thecombination of each of the CSI-RS configuration numbers #0 to #9 and thespread code {+1, −1}. In this case, V_(shift) for a cell having CellID=72 is mod(72, 20)=12. With this, the resource formed by combinationof the CSI-RS configuration number #2 and the spread code {+1, −1} whichcorresponds to V_(shift)=12 is specified as the resource for celldetection reference signal for the corresponding cell. The same appliesto other cell IDs.

Association as described above between the cell identification numbersand resources (resources corresponding to V_(shift)) is shared inadvance between the base station 100 and the terminal 200.

Furthermore, the base station 100 performs rate matching of a datasignal using the set transmission subframe information. Specifically,the base station 100, in the subframe indicated by the transmissionsubframe information, does not arrange any data in a resource fortransmitting the cell detection reference signal in other cell, andarranges data in remaining resources other than the resource fortransmitting the cell detection reference signal. With this, theterminal 200 can receive the cell detection reference signal withoutreceiving any interference from data of connection cells. The terminal200 thus can measure the reception signal power and the reception signalquality with good accuracy by using the cell detection reference signalsfor the surrounding cells. Furthermore, the terminal 200 can performreception and demodulation of data without receiving any interferencefrom the corresponding cell detection reference signal when detecting adata signal.

On the other hand, in the terminal 200, the reception processor 203receives the cell detection reference signal from each cell in thetransmission subframe indicated by the transmission subframe informationincluded in the setting information. The RRM report generator 206 thengenerates the RRM report using the cell detection reference signal.

As described above, the terminal 200 uses resources for CSI-RSs as aresource in which the cell detection reference signal can be arranged,and also grasps in advance the rule with the base station 100 that onlya part of the resources out of the resources for CSI-RSs is used as aresource for the cell detection reference signal. The terminal 200 thusmeasures only the resource for the cell detection reference signal whenthe terminal 200 measures the reception signal power and the receptionsignal quality by using the cell detection reference signal.

Furthermore, as described above, the terminal 200 grasps associationbetween a cell identification number (Cell ID) and a resource positionfor the cell detection reference signal. For example, when a cellidentification number and a resource are associated with each other inadvance, the terminal 200 specifies the cell identification number (CellID) from the resource position that has been detected and observes thecell detection reference signal in the resource corresponding to thespecified cell identification number. Alternatively, when the terminal200 has received in advance the cell identification number for the cellto be measured from the network, the terminal 200 may observe the celldetection reference signal only in the resource corresponding to theCSI-RS configuration number that corresponds to that cell identificationnumber.

The terminal 200 further receives transmission data from the basestation 100 in the subframe with the cell detection reference signalarranged therein. Thereafter, when the terminal 200 performsdemodulation and decoding of the transmission data, the terminal 200acknowledges that all of the above-described part of the resourcespredetermined as the resource for the cell detection reference signal orthe resource corresponding to the CSI-RS configuration numbercorresponding to the cell to be measured notified in advance is not usedfor data transmission. In other words, the terminal 200 performsoperations of demodulation and decoding of transmission data on theassumption that the transmission data is arranged in a resource otherthan the resource for the above-described cell detection referencesignal.

In this manner, in the present embodiment, the resource used forarranging the cell detection reference signal is to be only a part of aplurality of resources set for arranging an existing reference signal (aCSI-RS in the example in the present embodiment). This can prevent adrastic increase of the resource in which the cell detection referencesignal is arranged, in a subframe for transmitting the cell detectionreference signal, whereby lowering of the frequency use efficiency in asubframe in which the cell detection reference signal is arranged can beprevented.

In other words, the present embodiment can limit the resource usable forthe cell detection reference signal for detecting small cells arrangedat high density and avoid lowering of the frequency use efficiency atthe time of data transmission. This enables detection of small cellswhile suppressing the lowering of the frequency use efficiency at thetime of data transmission, whereby deployment of small cells at highdensity can be realized.

Furthermore, according to the present embodiment, it is predeterminedthat only a part of the resources out of the resources for an existingreference signal is used as a resource in which the cell detectionreference signal is arranged. This can simplify the cell detectionreference signal observing operations performed by the base station 100and the terminal 200, and at the same time, suppress lowering of thefrequency use efficiency in data transmission accompanied bytransmission of the corresponding reference signal.

Furthermore, according to the present embodiment, the resource for thecell detection reference signal is specified using a cell identificationnumber. This makes it unnecessary to add signaling for specifying theresource for the cell detection reference signal.

In the present embodiment, out of 20 resources represented by the 2-portCSI-RS configuration numbers (#0 to #19), the number of the candidateresources used as the resource for the cell detection reference signalis not limited to 10 (#0 to #9) as in the above-described example, andmay be other value (6, for example). Furthermore, out of 20 resourcesrepresented by the 2-port CSI-RS configuration numbers (#0 to #19), thenumber of the candidate resources used as the resource for the celldetection reference signal is not limited to a predetermined numbercounted from the smallest CSI-RS configuration number as describedabove. The candidate resources may be resources having even numbers orodd numbers for the CSI-RS configuration numbers thereof and may beresources represented by random CSI-RS configuration numbers, forexample. Furthermore, in the present embodiment, the resource in whichthe cell detection reference signal is arranged is not limited to aresource usable for 2-port CSI-RSs and may be a resource usable for4-port or 8-port CSI-RSs.

Variation A in First Embodiment

In the above-described embodiment, a case where the cell detectionreference signal is transmitted over the entire system has beendescribed. On the other hand, in a conventional LTE technique, aperformance code of cell detection has been stipulated based on aminimum value possibly employed as a system bandwidth. Specifically, ina performance code of cell detection, a transmission condition isstipulated under which predetermined accuracy can be obtained in asystem bandwidth of 6 RBs using 6 pieces of RBs illustrated in FIGS. 1Ato 1C. That is to say, when the cell detection reference signal istransmitted using the entire band in a generally-used wide systembandwidth (for example, 50 RBs), a larger number of samples and a widerbandwidth are used than those under the transmission conditionstipulated in the performance code of cell detection.

In the present variation, with the above-described point considered, anobject to be the above-described part of the resources used as theresource for the cell detection reference signal is defined to be abandwidth narrower than the system bandwidth. For example, as theresource for the cell detection reference signal, a resource (RB) thatis half for the system bandwidth may be used. With this, resources otherthan the resource used as the resource for the cell detection referencesignal can be utilized for data transmission, and the lowering of thefrequency use efficiency at the time of data transmission can be furtheravoided in the corresponding subframe. Furthermore, in the terminal 200,the resource to be subjected to observation of the cell detectionreference signal is limited, whereby an increase of the powerconsumption can be suppressed.

In the present variation, the resource used as the resource for the celldetection reference signal is not limited to half for the systembandwidth as long as the resource is for a bandwidth narrower than theentire system bandwidth. For example, 6 RBs described above may be set.

Furthermore, a bandwidth narrower than the system bandwidth, which hasbeen stipulated as described above, may be used to performfrequency-domain multiplexing on the cell detection reference signalsfor a plurality of cells. For example, when a resource (RB) that is halffor the system bandwidth is used as the resource for the cell detectionreference signal, in cell A, the cell detection reference signal may bearranged in a frequency position for a low frequency with a smaller RBnumber. Furthermore, in cell B, the cell detection reference signal maybe arranged in a frequency position for a high frequency with a largerRB number.

Furthermore, a cell identification number may be used also forspecifying a frequency position in which the cell detection referencesignal is arranged. For example, an integer value dividing the systembandwidth is set to N_(freq) and the number of candidates used as theabove-described part of the resources in which the cell detectionreference signal is arranged is set to 20 resources. In this case, thefrequency position in which the cell detection reference signal isarranged (the band for arranging) is specified as mod(Cell ID,N_(freq)), and the resource for the cell detection reference signal isspecified as mod(Cell ID/N_(freq), 20).

For specification of a frequency position used in the present variation,bandwidth parts determined for frequency selective CSI report can beapplied. This enables a cell detection operation using an existingmeasurement function in the terminal 200.

In this manner, frequency-domain multiplexing of the cell detectionreference signal of each cell is performed, whereby lowering of thefrequency use efficiency caused by the cell detection reference signalis prevented even in a case where small cells are arranged at highdensity (for example, 20 to 100 pieces).

Variation B in First Embodiment

In Variation A described above, a case where a large number of samplesof the cell detection reference signal is utilized for frequency-domainmultiplexing has been described. In the same manner, code-domainmultiplexing can be applied. That is to say, the present variationemploys, as an example, a configuration in which a plurality of celldetection reference signals are arranged using a spreading sequence inthe frequency direction and subjected to spread multiplexing. As thespread multiplexing in this case, for example, multiplexing performedwith a different cyclic shift assigned to a Zadoff-Chu sequence used ina 3GPP LTE system is considered. For another example, a configuration isemployed in which a plurality of cell detection reference signals arearranged using a spreading sequence in the time direction and subjectedto spread multiplexing. As the spread multiplexing in this case, forexample, multiplexing performed using a code with a different Walshsequence used in an LTE system is considered. Furthermore, the number ofcodes used for the spread multiplexing of the cell detection referencesignals is set to N_(code) and the number of candidates used as theabove-described part of the resources in which the cell detectionreference signal is arranged is set to 20 resources. In this case, theresources for the cell detection reference signals are specified asmod(Cell ID/N_(ode), 20), and a spread code applied for the celldetection reference signal is specified as mod(Cell ID, N_(code)).

In this manner, code-domain multiplexing of the cell detection referencesignal of each cell is performed, whereby lowering of the frequency useefficiency caused by the cell detection reference signal is preventedeven in a case where small cells are arranged at high density (forexample, 20 to 100 pieces).

Variation C in First Embodiment

In the embodiment described above, a case where an optional CSI-RSconfiguration number is used for limiting the CSI-RS resources in whichthe cell detection reference signal is arranged to a part of theresources has been described. By contrast, in the present variation,when the resource for the cell detection reference signal is limited,only a CSI-RS configuration number that corresponds to the resourcearranged in a second slot out of the slots forming the subframe is used.

For example, in a first slot of the subframe, an operation of thetransmission and reception system may be performed when the terminal 200returns from the DRX state. By contrast, in the present variation, theresource for the cell detection reference signal is limited to thesecond slot, whereby the terminal 200 can perform a cell detectionoperation with reduced influence of instability in the transmission andreception system immediately after returning from the DRX state.

Second Embodiment

The CSI-RS is also aimed at implementing a coordinated multipletransmission point (CoMP) function seeking for performance improvementwith a plurality of base stations performing coordinated operations.

Furthermore, for the terminal to observe with good accuracy a referencesignal (CSI-RS) transmitted from a transmission point (TP) that belongsto a plurality of base stations performing coordinated operations in theCoMP, a muting method is also provided, with which data at the TP, towhich the corresponding terminal is connected, is a non-transmissionsignal.

Specifically, out of the CSI-RS configuration numbers described above,each of the CSI-RS configuration numbers #0 to #9 (see FIG. 1B)corresponding to 4 ports is written in bitmap format. A mechanism isthen arranged by which the terminal is notified from the base station ofthe resource with which the CSI-RS is a non-transmission signal(non-transmission signal resource). Information in bitmap formatindicating which resource is the non-transmission signal resource isreferred to as a non-transmission CSI-RS configuration number list(zeroTxPowerResourceConfigList).

As an example, out of 10 resources represented by 4-port CSI-RSconfiguration numbers (resourceConfig) #0 to #9, it is assumed that 2resources represented by the CSI-RS configuration numbers #1 and #2 arenon-transmission signal resources. In this case, the non-transmissionCSI-RS configuration number list is {0, 1, 1, 0, 0, 0, 0, 0, 0, 0}.Here, in the order from the head bit of the non-transmission CSI-RSconfiguration number list, each bit corresponds to the CSI-RSconfiguration numbers #0 to #9. “1” represents a non-transmission signalresource, and “0” represents a resource other than the non-transmissionsignal resource.

The base station provides a notification of a transmission subframe(zeroTxPowerSubframeConfig) including a transmission cycle and an offsettogether with the above-described CSI-RSs in the non-transmission CSI-RSconfiguration number list. With this, the terminal can specify whichresource is the non-transmission signal resource in the correspondingsubframe. FIG. 6 illustrates a position (resource surrounded by a dottedline) of a non-transmission signal resource in a subframe correspondingto the non-transmission CSI-RS configuration number list (theabove-described example: {0, 1, 1, 0, 0, 0, 0, 0, 0, 0}) set to atransmission point to which a certain terminal is connected. The CSI-RSconfiguration of a transmission point positioned in the periphery of theabove-described transmission point (referred to as a peripheral TP) isassociated with any of the non-transmission signal resources (in FIG. 6,the CSI-RS configuration numbers #1 and #2), whereby the terminal is notinterfered with data from the transmission point connected thereto whenobserving a signal of the corresponding peripheral TP as a desiredsignal. This enables improvement in measurement accuracy of CSIs in theterminal.

In the same manner, when the CSI-RSs are used as the cell detectionreference signals also, a muting method can be applied to implementdetection of the cell detection reference signals from a plurality ofcells with good accuracy.

In the present embodiment, signaling of the non-transmission signalresource described above (zeroTxPowerResourceConfigList) is utilized toprovide a notification of the resource for the cell detection referencesignal. That is to say, in the present embodiment, out of the CSI-RSconfigurations for each number of ports illustrated in FIGS. 7A to 7C,the CSI-RS configuration number for 4 ports (resourceConfig, FIG. 7B) inwhich signaling of a non-transmission signal resource is stipulated isused to provide a notification of the resource for the cell detectionreference signal.

The basic configurations of the base station and the terminal accordingto the present embodiment are common with the base station 100 and theterminal 200 according to the first embodiment. For this reason, FIGS. 4and 5 are used for the description of the base station and the terminalaccording to the present embodiment.

The base station 100 according to the present embodiment generatestransmission subframe information indicating a subframe for transmittingthe cell detection reference signal with respect to the terminal 200 tobe set, in the same manner in the first embodiment.

Furthermore, the base station 100 uses only a preset part of theresources out of the resources in which the cell detection referencesignal can be arranged, as a resource for the cell detection referencesignal. Specifically, the base station 100 uses a resource set as anon-transmission signal resource out of the resources for CSI-RSs as aresource for the cell detection reference signal. The non-transmissionCSI-RS configuration number list is notified from the base station 100to the terminal 200.

On the other hand, the terminal 200 (reception processor 203) receivesthe non-transmission CSI-RS configuration number list indicating thenon-transmission signal resource for setting a CSI-RS tonon-transmission at the base station (transmission point) to which theterminal 200 is connected, out of a plurality of resources for CSI-RSs.The terminal 200 uses a resource indicated in the non-transmissionCSI-RS configuration number list described above out of the resourcesfor CSI-RSs as a resource for the cell detection reference signal. Inother words, in the present embodiment, out of a plurality of resourcesfor CSI-RSs, a candidate resource for arranging the cell detectionreference signal is a resource for setting a CSI-RS indicated in thenon-transmission CSI-RS configuration number list to non-transmission.

For example, out of 10 CSI-RS configuration numbers (#0 to #9illustrated in FIG. 1B, a part surrounded by a bold line illustrated inFIG. 7B), which can be used as resources for 4-port CSI-RSs, it isassumed that the CSI-RS configuration numbers #0, #1, and #4 are set tonon-transmission signal resources. In this case, the non-transmissionCSI-RS configuration number list (zeroTxPowerResourceConfigList) is {1,1, 0, 0, 1, 0, 0, 0, 0, 0}.

In this case, the base station 100 and the terminal 200 use any ofresources formed by combination of 3 resources set to thenon-transmission signal resources (CSI-RS configuration numbers #0, #1,and #4) and 2 types of spread codes multiplexing 2 ports ({+1, +1}, {+1,−1}) as the resource for the cell detection reference signal.

The port numbers 0 to 7 illustrated in FIGS. 7A to 7C correspond toCSI-RS port numbers 15 to 22 respectively. For example, the port numbers0 and 2 (the CSI-RS port numbers 15 and 17) correspond to the spreadcode {+1, +1}, and the port numbers 1 and 3 (the CSI-RS port numbers 16and 18) correspond to the spread code {+1, −1}.

As an example, the base station 100 and the terminal 200 use only 6resources corresponding to the port numbers 0 and 2 (that is, the CSI-RSport numbers 15 and 17) of the CSI-RS configuration numbers(resourceConfig) #0, #1, and #4 illustrated in FIG. 7B (in other words,resources corresponding to the spread code {+1, +1}; resourcessurrounded by dotted frames illustrated in FIG. 7B) as the resources forthe cell detection reference signal.

In FIG. 7B, V_(shift)=0 is associated with the combination of the CSI-RSconfiguration number #0 and the port number 0, and V_(shift)=1 isassociated with the combination of the CSI-RS configuration number #0and the port number 2. In the same manner, V_(shift)=2 is associatedwith the combination of the CSI-RS configuration number #1 and the portnumber 0, and V_(shift)=3 is associated with the combination of theCSI-RS configuration number #1 and the port number 2. Furthermore,V_(shift)=4 is associated with the combination of the CSI-RSconfiguration number #4 and the port number 0, and V_(shift)=5 isassociated with the combination of the CSI-RS configuration number #4and the port number 2. The above-described association between V_(shift)and each resource is grasped by the base station 100 and the terminal200 in advance.

In this case, the terminal 200 specifies a resource corresponding toV_(shift) obtained by using a cell identification number (Cell ID) toset 2*mod(Cell ID/2, 3)+mod(Cell ID, 2) as the resource for the celldetection reference signal. It should be noted that in the function inthe above-described formula, “Cell ID/2” represents a value obtained byrounding down the decimal places of a value obtained by dividing theCell ID by 2. As an example, V_(shift) obtained by setting 2*mod(36,3)+mod(72, 2) to a cell having Cell ID=72 is 0, and a resource formed bycombination of the CSI-RS configuration number #0 and the port number 0,which correspond to V_(shift)=0, is specified as the resource for celldetection reference signal of the corresponding cell. As anotherexample, V_(shift) obtained by setting 2*mod(36, 3)+mod(73, 2) to a cellhaving Cell ID=73 is 1, and a resource formed by combination of theCSI-RS configuration number #0 and the port number 2, which correspondto V_(shift)=1, is specified as the resource for cell detectionreference signal of the corresponding cell. In the same manner,V_(shift) obtained by setting 2*mod(37, 3)+mod(74, 2) to a cell havingCell ID=74 is 2, and a resource formed by combination of the CSI-RSconfiguration number #1 and the port number 0, which correspond toV_(shift)=2, is specified as the resource for cell detection referencesignal of the corresponding cell. The same applies to other cell IDs.

In the description above, a structure for representing a resource forthe cell detection reference signal uses the port numbers 0 and 2(CSI-RS ports 15 and 17), that is, the spread code {+1, +1}. However,the structure is not limited thereto, and may be a structure using theport number 1 and 3 (CSI-RS ports 16 and 18), that is, the spread code{+1, −1} or may be a structure using the spread code {+1, +1} and thespread code {+1, −1} in combination.

Furthermore, the terminal 200 may specify a resource corresponding toV_(shift) obtained by using a cell identification number (Cell ID) toset mod(Cell ID, 6) instead of 2*mod(Cell ID/2, 3)+mod(Cell ID, 2) asthe resource for the cell detection reference signal.

In this manner, in the present embodiment, an existing non-transmissionsignal resource signaling is used to provide a notification of a part ofthe CSI-RS resources used as the resource for the cell detectionreference signal. That is to say, notification of the resource for thecell detection reference signal can be bitmap notification of the CSI-RSconfiguration number for the 4-port CSI-RS in the non-transmissionCSI-RS configuration number list for providing a notification of theresource with a non-transmission signal for data transmission in asubframe for transmitting the cell detection reference signal.

This configuration according to the present embodiment uses an existingnon-transmission signal resource signaling to provide a notification ofthe resource for the cell detection reference signal from the basestation 100 to the terminal 200, whereby addition of new signaling forproviding a notification of the resource for the cell detectionreference signal is unnecessary.

Furthermore, according to the present embodiment, the resource for thecell detection reference signal is limited to a resource notified as anon-transmission signal resource, out of a plurality of resources set tothe CSI-RSs. This can prevent a drastic increase of the resource inwhich the cell detection reference signal is arranged and therebyprevent lowering of the frequency use efficiency in the correspondingsubframe. That is to say, the present embodiment enables prevention ofthe lowering of the frequency use efficiency in a subframe in which thecell detection reference signal is arranged, as in the first embodiment.

Third Embodiment

In the present embodiment, a case where CoMP control is performed willbe described.

The basic configurations of the base station and the terminal accordingto the present embodiment are common with the base station 100 and theterminal 200 according to the first embodiment. For this reason, FIGS. 4and 5 are used for the description of the base station and the terminalaccording to the present embodiment.

FIG. 8 illustrates a transmission point to be subjected to CoMP control(referred to as a CoMP measurement set in some cases) and the terminal200. In FIG. 8, a configuration is employed in which coordinatedtransmission and reception with respect to the terminal is supported bya macro eNB (macro cell) and LPNs 1 to 3 (small cells). That is to say,the terminal 200 (reception processor 203) receives a data signaltransmitted through a coordinated operation of a plurality oftransmission points (the macro eNB and the LPNs 1 to 3). Furthermore, inFIG. 8, the terminal 200 is connected to the LPN1.

As illustrated in FIG. 8, the macro eNB and the LPNs 1 to 3 transmitcell detection reference signals to the terminal 200. The terminal 200generates an RRM report using the cell detection reference signalsreceived from each cell and feeds back the generated RRM report to thenetwork through the LPN1 connected thereto.

A method of specifying the resource for a cell detection referencesignal according to the present embodiment will be described below.

In the description below, as an example, a case where a resource for aCSI-RS is used as the resource for a cell detection reference signalwill be described.

Furthermore, in the description below, a transmission point to besubjected to CoMP control is assigned with the same cell identificationnumber (Cell ID) (in FIG. 8, Cell ID: A) and a transmission pointidentification number (TP ID) different from each other is set (in FIG.8, TP ID: X, Y, Z, W).

Furthermore, similarly to the first embodiment, as the resources set forthe CSI-RS, 40 resources in total, that are composed by multiplicationof two types of spread codes ({+1, +1}, {+1, −1}) for multiplexing twoports with each of the resources represented by the CSI RS configurationnumbers and other 20 resources usable for 2-port CSI-RSs represented bythe CSI-RS configuration numbers (#0 to #19 illustrated in FIG. 1C), areused. In this case, only 20 resources in total that include the CSI-RSs#0 to #9 and the resources formed by combination with two types ofspread codes are used as the resources for the cell detection referencesignal (candidate resources), as in the first embodiment.

In this case, the base station 100 and the terminal 200 specifyresources in each of which the cell detection reference signaltransmitted from each transmission point is arranged, based on the cellidentification number (Cell ID) and the transmission pointidentification number (TP ID) for each transmission point, out of theresources for the cell detection reference signal (candidate resources).For example, the resource for the cell detection reference signal foreach of the transmission points is specified as a resource correspondingto a value (V_(shift)) (V_(shift)=0 to 19) obtained by using the cellidentification number and the transmission point identification numberto set mod(4*mod(Cell ID, 20)+mod(TP ID, 4), 20).

For example, as in the first embodiment, it is assumed that V_(shift)=0to 9 is respectively associated with the combination of each of theCSI-RS configuration numbers #0 to #9 and the spread code {+1, +1}, andV_(shift)=10 to 19 is respectively associated with the combination ofeach of the CSI-RS configuration numbers #0 to #9 and the spread code{+1, −1}. Furthermore, for example, in FIG. 8, it is assumed that CellID: A=72, TP ID: X=0, Y=1, Z=2, W=3. In this case, the terminal 200, asa position of the resource for the cell detection reference signal,specifies a resource corresponding to V_(shift)=mod(4*12+0, 20)=8 withrespect to the macro eNB, specifies a resource corresponding toV_(shift)=mod(4*12+1, 20)=9 with respect to the LPN1, specifies aresource corresponding to V_(shift)=mod(4*12+2, 20)=10 with respect tothe LPN2, and specifies a resource corresponding toV_(shift)=mod(4*12+3, 20)=11 with respect to the LPN3.

In the same manner, in FIG. 8, it is assumed that Cell ID: A=73, TP ID:X=0, Y=1, Z=2, W=3. In this case, the base station 100 and the terminal200, as a position of the resource for the cell detection referencesignal, specifies a resource corresponding to V_(shift)=mod(4*13+0,20)=12 with respect to the macro eNB, specifies a resource correspondingto V_(shift)=mod(4*13+1, 20)=13 with respect to the LPN1, specifies aresource corresponding to V_(shift)=mod(4*13+2, 20)=14 with respect tothe LPN2, and specifies a resource corresponding toV_(shift)=mod(4*13+3, 20)=15 with respect to the LPN3.

In this manner, the resource for the cell detection reference signaltransmitted from each cell is uniquely specified based on the Cell IDand the TP ID.

The base station 100 arranges the cell detection reference signal in aresource position specified in the above-described manner from eachtransmission point to transmit a transmission signal.

The terminal 200 uses a cell identification number separately acquiredand attempts a measurement operation for the cell detection referencesignal in the resource corresponding to the candidate transmission pointthat is possible, and thereby specifies the transmission point that hastransmitted the corresponding signal. The terminal 200 then measures thereception signal power and the reception signal quality of the celldetection reference signal transmitted from the specified transmissionpoint and reports the measured reception signal power and receptionsignal quality to the base station 100 as an RRM report.

In this manner, according to the present embodiment, the base station100 and the terminal 200 specify a position of the resource for the celldetection reference signal using both cell identification number andtransmission point identification number when coordinated transmissionis performed. With this, even when coordinated transmission isperformed, lowering of the frequency use efficiency can be prevented ina subframe for transmitting the cell detection reference signal as inthe first embodiment, and at the same time, the resource correspondingto each transmission point can be specified in the terminal 200.

Each of the embodiments according to the present disclosure has beendescribed above.

Other Embodiment

In each of the embodiments described above, a case has been describedwhere a part of a plurality of resources for arranging the CSI-RSs isused as a resource for arranging the cell detection reference signal.That is to say, by using a part of the resources for the CSI-RSs as aresource for the cell detection reference signal, a number of candidatesequal to that of existing RRM signals can be secured by using a part ofthe resources that can be set to the CSI-RSs. However, the referencesignal resource for arranging the cell detection reference signal is notlimited to the resource for the CSI-RS. For example, a PRS may be usedas the cell detection reference signal. That is to say, by using aresource for the PRS as the resource for the cell detection referencesignal, a signal pattern of the

PRS which is excellent in frequency synchronization and timingsynchronization can be used as the cell detection reference signal. Theterminal 200 can then detect a plurality of cells using a specifiedresource. Alternatively, a reduced PSS/SSS+CRS may be used as the celldetection reference signal.

In each of the embodiments described above, an antenna port indicates alogical antenna including one or a plurality of physical antennas. Thatis to say, an antenna port does not necessarily indicate one physicalantenna and may indicate an array antenna including a plurality ofantennas, for example.

For example, in a 3GPP LTE system, the number of physical antennasforming an antenna port is not stipulated and an antenna port is onlystipulated as a minimum unit that a base station can transmit differentreference signals.

Furthermore, an antenna port may be stipulated as a minimum unit formultiplying the weighting of precoding vector.

In each of the embodiments described above, a case where the embodimentof the present disclosure is configured by hardware has been describedas an example.

However, the embodiment of the present disclosure can be implemented bysoftware in cooperation with hardware.

Furthermore, each of the functional blocks used in the description ofthe embodiments is typically implemented as an LSI being an integratedcircuit. Each of the functional blocks may be made into one chipindividually, or a part or all of the functional blocks may be made intoone chip. Although an LSI is herein assumed, the LSI may be referred toas an IC, a system LSI, a super LSI, and an ultra LSI, depending on thedifference in the degree of integration.

Furthermore, the method of circuit integration is not limited to usingan LSI, and a dedicated circuit or a general purpose processor may beused. A field programmable gate array (FPGA) which is programmable aftermanufacturing of an LSI or a reconfigurable processor of which theconnection of circuit cells inside and the settings are reconfigurablemay be used.

Furthermore, when a technique of circuit integration replacing an LSIappears due to the progress of the semiconductor technology or anothertechnology derived therefrom, the technique naturally may be used forintegration of the functional block. Application of biotechnology, forexample, is possible.

The terminal according to the present disclosure includes a receptionprocessor, a generator, and a transmission processor. The receptionprocessor receives first reference signals, each of the first referencesignals being transmitted from corresponding one of a plurality of cellsand being a reference signal for cell detection that is mapped to anyone of a plurality of candidate resources, which are a part of aplurality of resources set for second reference signals in a subframe.The generator generates measurement information indicating a measurementresult of reception quality measured using the received first referencesignals. The transmission processor transmits the generated measurementinformation.

In the terminal according to the present disclosure, the receptionprocessor specifies resources to which the first reference signalstransmitted from the plurality of cells are mapped, among the pluralityof candidate resources, based on a cell identification number of each ofthe plurality of cells.

In the terminal according to the present disclosure, the receptionprocessor further receives control information indicatingnon-transmission resources on which the second reference signals tarenot to be transmitted by a base station connected with the terminal,among the plurality of resources set for the second reference signals.The plurality of candidate resources are the non-transmission resourcesindicated by the control information.

In the terminal according to the present disclosure, the receptionprocessor further receives a data signal transmitted through coordinatedtransmission by a plurality of transmission points and, based on a cellidentification number and a transmission point identification number ofeach of the plurality of transmission points, specifies the resources towhich the first reference signals transmitted from each of the pluralityof transmission points are mapped, out of the plurality of candidateresources.

In the terminal according to the present disclosure, the secondreference signals are reference signals for measuring channelinformation.

In the terminal according to the present disclosure, the secondreference signals are reference signals for measuring a position of theterminal.

The base station according to the present disclosure includes a settingcircuitry, a transmission processor, and a reception processor. Thesetting circuitry sets a subframe to which first cell detectionreference signals are mapped. Each of the first reference signals aremapped to any one of a plurality of candidate resources, which are apart of a plurality of resources set for second reference signals in thesubframe. The transmission processor transmits subframe informationindicating the subframe. The reception processor receives measurementinformation indicating a measurement result of reception qualitymeasured using the first reference signals.

A transmission method according to the present disclosure includesreceiving, generating, and transmitting. The receiving receives firstreference signals, each of the first reference signals being transmittedfrom corresponding one of a plurality of cells. The first referencesignals are reference signal for cell detection that is mapped to any ofa plurality of candidate resources , which are a part of a plurality ofresources set for second reference signals in to subframe. Thegenerating generates measurement information indicating a measurementresult of reception quality measured using the received first referencesignal. The transmitting transmits the measurement information.

A reception method according to the present disclosure includes setting,transmitting, and receiving. The setting sets a subframe to which firstreference signals are mapped. Each of the first reference signals aremapped to any one of a plurality of candidate resources, which are apart of a plurality of resources set for second reference signals in thesubframe. The transmitting transmits subframe information indicating thesubframe. The receiving receives measurement information indicating ameasurement result of reception quality measured using the firstreference signals.

The present disclosure is useful for a mobile communication system andthe like.

1. A base station comprising: a transmitter, which, in operation, transmits Channel State Information Reference Signals (CSI-RSs) in a subframe, wherein a first portion of resources assigned to the CSI-RSs in the subframe are non-transmission resources for the CSI-RSs, a second portion of the resources assigned to the CSI-RSs in the subframe are transmission resources for the CSI-RSs, discovery signals are transmitted from one or more cells for cell detection in the first portion of resources, and the first portion of the resources are determined based on a cell identification number of the one or more cells; and a receiver, which, in operation, receives a measurement report indicating a measurement result of reception quality measured using the discovery signals.
 2. The base station according to claim 1, wherein the transmitter, in operation, transmits control information indicating the non-transmission resources for the CSI-RSs.
 3. The base station according to claim 2, wherein the control information indicates the non-transmission resources of a plurality of resources in a time domain and in a frequency domain.
 4. The base station according to claim 2, wherein the control information indicates the non-transmission resources in the subframe.
 5. The base station according to claim 1, wherein the discovery signals are transmitted over an entire system band.
 6. The base station according to claim 1, wherein the discovery signals are transmitted over a bandwidth which is narrower than an entire system band.
 7. The base station according to claim 1, wherein the CSI-RSs are reference signals for measuring a position of a communication apparatus.
 8. The base station according to claim 1, wherein the transmitter, in operation, transmits control information indicating the cell identification number of the one or more cells.
 9. A communication method implemented in a base station, the communication method comprising: transmitting Channel State Information Reference Signals (CSI-RSs) in a subframe, wherein a first portion of resources assigned to the CSI-RSs in the subframe are non-transmission resources for the CSI-RSs, a second portion of the resources assigned to the CSI-RSs in the subframe are transmission resources for the CSI-RSs, discovery signals are transmitted from one or more cells for cell detection in the first portion of resources, and the first portion of the resources are determined based on a cell identification number of the one or more cells; and receiving a measurement report indicating a measurement result of reception quality measured using the discovery signals.
 10. The communication method according to claim 9, further comprising: transmitting control information indicating the non-transmission resources for the CSI-RSs.
 11. The communication method according to claim 10, wherein the control information indicates the non-transmission resources of a plurality of resources in a time domain and in a frequency domain.
 12. The communication method according to claim 10, wherein the control information indicates the non-transmission resources in the subframe.
 13. The communication method according to claim 9, wherein the discovery signals are transmitted over an entire system band.
 14. The communication method according to claim 9, wherein the discovery signals are transmitted over a bandwidth which is narrower than an entire system band.
 15. The communication method according to claim 9, wherein the CSI-RSs are reference signals for measuring a position of a communication apparatus.
 16. The communication method according to claim 9, further comprising: transmitting control information indicating the cell identification number of the one or more cells. 